Micromechanics simulations of glass–estane mock polymer bonded explosives

Abstract

Polymer bonded explosives (PBXs) are particulate composites containing explosive particles and a continuous binder. The elastic modulus of the particles, at room temperature and higher, is often three to four orders of magnitude higher than that of the binder. Additionally, the explosive particles occupy high volume fractions, often greater than 90%. Both experimental and numerical determination of macroscopic properties of these composites is difficult. High modulus contrast mock PBXs provide a means of relatively inexpensive experimentation and validation of numerical approaches to determine properties of these materials. The goal of this investigation is to determine whether the effective elastic properties of monodisperse glass-estane mock PBXs can be predicted from two-dimensional micromechanics simulations using the finite element (FEM) method. In this study, the effect of representative volume element (RVE) size on the prediction of two-dimensional properties is explored. Two-dimensional estimates of elastic properties are compared with predictions from three-dimensional computations and with experimental data on glass-estane composites containing three different volume fractions of spherical glass beads. The effect of particle debonding on the effective elastic properties is also investigated using contact analyses. Results show that two-dimensional unit cells containing 10-20 circular particles are adequate for modelling glass-estane composites containing less than 60% glass particles by volume. No significant difference is observed between properties predicted by the two-and three-dimensional models. FEM simulations of RVEs, containing particles that are perfectly bonded to the binder, produce estimates of Young's modulus that are higher than the experimental data. Incorporation of debonding between particles and the binder causes the effective Young's modulus to decrease. However, the results suggest that cracks in the composite may play a 3 Author to whom correspondence should be addressed.

Prediction of effective thermo-mechanical properties of particulate composites

“…In the first (Method I), the particle volume percentage in the two-dimensional RVEs is maintained identical to the three-dimensional ones while the particle distribution varies. The efficacy of this simplification has been demonstrated by Banerjee et al [10]. In the second approach (Method II), twodimensional RVEs are generated by slicing the three-dimensional ones along different cross-sections (as shown in Figure 2).…”

“…The benchmark problem considered for validating the RVE model is the prediction of effective elastic properties of a glass-estane composite [10]. The particle concentrations chosen for comparison, 21% and 59%, are the two extrema considered by Banerjee et al [10].…”

“…The particle concentrations chosen for comparison, 21% and 59%, are the two extrema considered by Banerjee et al [10]. The results are also compared at extrema for strain rates, 0.001s -1 and 2400s -1 .…”

“…Estane was treated as isotropic with the Young's modulus being a function of temperature and strain rate as summarized in Table 2; a Poisson's ratio of 0.49 was used. The glass beads were modeled as an isotropic material with constant elastic properties over the entire spectrum of strain rates and temperatures considered [10]. A Young's modulus of 50,000…”

“…An improved model was proposed by Clements and Mas [9] to investigate the mechanical behavior of PBX with a bimodal particle distribution. Using a two-dimensional representative volume element (RVE), Banerjee and co-workers investigated the effective elastic properties of the particulate explosive PBX 9501 [10,11]. In most of these efforts, the random distribution of particles in the unit cell, which is crucial to property prediction, is either ignored [8,9] or manually controlled [10,11].…”